Selective sorting of hexane isomers by anion-functionalized metal-organic frameworks with optimal energy regulation

Extensive efforts have been made to improve the separation selectivity of hydrocarbon isomers with nearly distinguishable boiling points; however, how to balance the high regeneration energy consumption remains a daunting challenge. Here we describe the efficient separation of hexane isomers by constructing and exploiting the rotational freedom of organic linkers and inorganic SnF62− anions within adaptive frameworks, and reveal the nature of flexible host-guest interactions to maximize the gas-framework interactions while achieving potential energy storage. This approach enables the discrimination of hexane isomers according to the degree of branching along with high capacity and record mono-/di-branched selectivity (6.97), di-branched isomers selectivity (22.16), and upgrades the gasoline to a maximum RON (Research Octane Number) of 105. Benefitting from the energy regulation of the flexible pore space, the material can be easily regenerated only through a simple vacuum treatment for 15 minutes at 25 °C with no temperature fluctuation, saving almost 45% energy compared to the commercialized zeolite 5 A. This approach could potentially revolutionize the whole scenario of alkane isomer separation processes.

1. Clarity of the Main Idea: The manuscript lacks a clear and cohesive presentafion of the central concept.The intended approach involves combining an energy-efficient MOF containing anionfuncfionalifies (ZU-72) in the front, along with well-studied high performing sieves (SIFSIX-1-Cu or ZU-61) in the rear.This strategic combinafion aims to facilitate hexane isomer separafion while enhancing energy efficiency.However, the key fact is that the isomer separafion was conducted with SIFSIX-1, which has been widely studied.It is crucial to revise the introducfion and fitle to accurately convey the focus of the research and align them with the actual content of the manuscript.This will prevent potenfial confusion among readers, although the impact of the new framework is diluted inevitably.2. Introducfion Clarity: A significant improvement is needed in explaining the characterisfics of the MOFs discussed in the paper-ZU-72, SIFSIX-1-Cu, and ZU-61.Providing clear differenfiafions among these MOFs will help readers comprehend the subsequent research content.To enhance the manuscript's readability and coherence, make sure to establish a solid foundafion by outlining the unique features of each MOF in the introducfion.

Novelty and Comparafive Analysis:
To highlight the novelty of ZU-72, which adds to the anionfuncfionalized MOF (SIFSIX series) literature, the authors must emphasize its disfincfive aftributes.

Comments from Reviewer 1:
This manuscript reports three SIFSIX-based MOFs showing the good performance for separation of alkane isomers.The investigated MOF SNFSIX-2-Cu-i outperform the commercialized zeolite 5A and certain reported MOF materials for the separation of mono-and dibranched alkane isomers.There are studies for the discrimination of branched alkanes from linear alkanes that have been reported, e.g.those by Jing Li's group.Interestingly, were found to separate the challenging 22DMB and 23DMB, in which SIFSIX-1-Cu showed high capacity and excellent di-branched isomers selectivity, further improving the research octane numbers (RONs) of gasoline.The authors have carried out comprehensive experimental characterization for evaluating separation performances of those MOF materials.There is now one major concern on the collected amount of alkanes with qualified RONs (e.g.>92 or 95, during one breakthrough option).And how about this data in comparing with other adsorbent materials?There are also some issues needed be addressed: Response: We thank this reviewer for these positive and constructive comments which by addressing have allowed us to improve the manuscript.As suggested, we have calculated the collected amount of alkanes with qualified RONs (>95) on SNFSIX-2-Cu-i (ZU-72) to be 15.8 mL g -1 .And for comparison with other adsorbents, we have screened nearly all recent achievements in the separation of five-component hexane isomers and listed the separation performance in the revised Table S1.However, NU-2200, NU-2000, NU-2004 were not tested for the actual experimental breakthrough separations, while Al-bttotb and UU-200 did not provide the complete breakthrough separation conditions, so we were unable to calculate the exact collected amount of alkanes with qualified RONs.Therefore, in this work, we just compared the separation selectivity of SNFSIX-2-Cu-i with these materials, and SNFSIX-2-Cu-i exhibited benchmark selectivity (Figure 2c).Fortunately, Fe2(BDP)3 provides the separation conditions, we compared SNFSIX-2-Cu-i with Fe2(BDP)3 and SIFSIX-2-Cu-i, ZU-62 studied in this work.As shown in following Figure S32, SNFSIX-2-Cu-i exhibits the highest productivity of high-quality gasoline (RON>95).

Response:
We appreciate the constructive comments from the reviewer.The collected amounts of gasoline in this work, also known as the productivity of an adsorbent, is an important criterion for evaluating the performance of the adsorbent and should be carefully estimated.As suggested, we have calculated the collected amounts of highest quality gasoline with RON of 105 using SIFSIX-1-Cu to be 55.6 mL g -1 .However, currently there is no reported exploration on the separation of challenging 22DMB and 23DMB to obtain the highest quality gasoline.Thus, we have not compared this performance factor with other adsorbents.
Modification: Main text, page 7, line 170-172, added text "The following desorption operations enabled the further upgrading of gasoline with the highest RON (~105) (Figure 3c and Figure S35), with a productivity of 55.6 mL g -1 " 2. In order for the readership to better understand RON, please indicate in the supporting information how to calculate RON form the eluted mixture in Breakthrough experiments.
Response: As suggested, the detailed calculation of the RON from the eluted mixture in breakthrough experiments has been added in the revised Supplementary Information.
Modification: Supplementary Information, page 4, line 123-137, added the text: "The calculation of research octane numbers RONs from the eluted mixture in Breakthrough experiments Firstly, the prepared mixed gases of nHEX/2MP/3MP/23DMB/22DMB (1/1/1/1/1) was monitored by the gas chromatography, and the peak area of each component was recorded as S0 n , where n=1, 2, 3,4,5 represents nHEX, 2MP, 3MP, 23DMB and 22DMB respectiviely.Then the outlet gas from the column was monitored by the gas chromatography and the peak area of each component was recorded as S n ,where n=1, 2, 3,4,5 represents for nHEX, 2MP, 3MP, 23DMB and 22DMB respectively.Therefore, the concentration of each component (C n ) can be calculated using the following equation (1): The RON of nHEX, 2MP, 3MP, 23DMB and 22DMB are 30, 74, 75, 94 and 105 respectively, therefore the RON of the outlet mixture gas can be calculated using the following quation (2): 3. The authors explain that SIFSIX-1-Cu has a size exclusion effect, but do not provide a suitable explanation on size comparison, i.e. giving information about the pore size, etc.

Response:
We appreciate the constructive comments from the reviewer.The pore information and crystal structure of SIFSIX-1-Cu have been added to the revised manuscript and Supplementary Information.The molecular sizes of 22DMB and 23DMB are 8.0 x 6.7 x 5.9 Å 3 and 7.8 x 6.7 x 5.3 Å 3 , respectively.As shown in the following Figure S2, the pore size of SIFSIX-1-Cu falls within the range of 6.8 Å -7.2 Å, potentially resulting in a size exclusion effect for the relative larger molecule of 22DMB (8.0 x 6.7 x 5.9 Å 3 ).Additionally, the crystal size of SIFSIX-1-Cu is in the micrometer range, with dimensions reaching up to 15 µm (Figure S3).Such large crystal sizes would hinder the diffusion of molecules with sizes similar to the pores and enhance the size exclusion effect.Therefore, as demonstrated by the single-component equilibrium isotherm (Figure 2b), differential scanning calorimetry experiments (Figure S18), dynamic adsorption tests (Figure S19), and actual breakthrough tests (Figure 3b), 22DMB cannot enter the pore of SIFSIX-1-Cu, resulting in the molecular sieving effect for 22DMB.The corresponding discussion have been added in the revised manuscript.
3) Figure S2 and S3 have been added in the revised Supplementary Information.
Response: We thank this reviewer for the important comments.As suggested, we have included some flexible MOFs reported to have inherent thermal management in the introduction section and compare in result section.

Table S1 .
has been updated in the revised Supplementary Information Comparison of the uptake and selectivity of hexane isomers on various materials for five-component isomers separation